In the relevant technical field of the present invention, arms for spectacles are known which are made of thermoplastic or thermosetting polymeric material. In the continued search for new solutions, both functional and aesthetic, a requirement has arisen in this field for making spectacle arms of composite material comprising a polymeric matrix in which reinforcing fibres are embedded.
In particular there is a requirement for producing arms for spectacles in composite material where the reinforcing fibres are of the long fibre type and are present in a high proportion, in a percentage of at least 50% and up to 70% by weight.
This type of material, in itself, exhibits optimum mechanical characteristics and an aesthetic appearance which renders its use in the production of spectacle arms particularly attractive. However, it is decidedly lacking from the point of view of the flexing capacity, easily resulting in breakages when subjected even to limited flexing movements.
It is required, however, that spectacle arms should exhibit optimum flexibility characteristics both in order to adapt to the best possible extent to the various shapes of the heads of the users, and in order to withstand, without breaking into pieces, the stresses and/or impacts to which a pair of spectacles may be subjected during normal use. In order to increase the resilience of the known arms it is furthermore known to provide suitable resilient return devices, which act on the articulation between the arm and the front frame of the spectacles, and which allow the arms to be resiliently deflected with respect to a predefined open position. Of course, the provision of devices of the type indicated above has a significant effect on the production costs.
A further drawback connected with the use of composite material lies in the fact that it is chemically poorly compatible with the common thermoplastic and elastomeric polymeric materials used in the field, so that it would be difficult, for example, to overmould an element made of polyolefin or polyamide material onto a arm made of composite material, because of the lack of adhesion between the two materials.
A further drawback connected with the use of composite materials lies in the possibility of producing splinters and having sharp edges in the event of breakage.